1. Field of the Invention
The present invention relates to a molding compound containing a phenol resin and a carbon powder, which is preferably used to mold parts for electric and electronic devices.
2. Disclosure of the Prior Art
In the past, various molding compounds have been used to mold parts for electric and electronic devices. For example, as disclosed in Japanese Patent Early Publication No. 9-87417, a housing or casing for electronic devices needs high electrical conductivity. In addition, Japanese Patent Early Publications No. 2001-31880 and No. 2001-122663 describe that a heat sink for electronic devices needs high thermal conductivity. In these applications, good mechanical strength is also needed.
As the molding compound with the above properties, a molding compound containing a carbon powder and a phenol resin has been known in the past. The phenol resin can be generally obtained by reacting a phenol with a formaldehyde in the presence of a basic catalyst. The phenol resin is mixed and kneaded with the carbon powder, and then a resultant mixture is dried and ground to obtain a powder of the molding compound. By molding the powder of this molding compound in a desired shape at a heating temperature under a pressure, it is possible to obtain molded articles as the parts for electric and electronic devices.
However, this molding compound usually contains a relatively large amount of the phenol resin, i.e., 30 to 40 wt %. As the content of the phenol resin decreases, it becomes difficult to obtain molded articles, in which the carbon powder is uniformly dispersed, because a surface of the carbon powder can not be sufficiently coated with the phenol resin. From this reason, such a large amount of the phenol resin is needed. On the other hands as the content of the phenol resin increases, the bending strength of the molded articles is improved. However, since an amount of the carbon powder in the molding compound relatively decreases, there is a problem of deteriorating the thermal conductivity and the electrical conductivity of the molded articles.